A research team also noticed monkeys in captivity expend the same amount of energy as their peers in the wild; this suggests daily physical activity has less to do with energy expenditure than was previously believed, a Lincoln Park Zoo news release reported per HNGN.Most mammals age faster and live much shorter lives than humans and primates. Common household pets such as dogs and cats reach adulthood in months and die by the time they reach their teen years. Humans and primates also reproduce less often than other animals, and have long childhoods and lives.

A research team looked at daily energy expenditure of 17 primate species in both captivity and the wild. The team had hopes to discover a link between a slower immune system and longevity.

The scientists used a non-invasive technique called “doubly labeled water,” which tracks the body’s carbon dioxide production. The team was able to measure how many calories were burned in each subject over the span of ten days.

“The results were a real surprise,” Herman Pontzer, an anthropologist at Hunter College in New York and the lead author of the study, said. “Humans, chimpanzees, baboons, and other primates expend only half the calories we’d expect for a mammal. To put that in perspective, a human — even someone with a very physically active lifestyle — would need to run a marathon each day just to approach the average daily energy expenditure of a mammal their size.”

This was the first time scientists had noticed reduction in metabolic rate in primates. Energy expenditure is connected to aging. The primate’s slow metabolisms and long lives may have been shaped by evolution.

“The environmental conditions favoring reduced energy expenditures may hold a key to understanding why primates, including humans, evolved this slower pace of life,” David Raichlen, an anthropologist at the University of Arizona and a coauthor of the study, said.